Vice presidential debate: Seven things you need to know

Vice presidential debates are one of American democracy's enduring quirks. Held in one of the hottest political spotlights on the major issues of the day, they feature two of the less-important candidates on the national stage in a debate that usually doesn't change the race much. Here are seven facts about vice presidential debates you should know before tuning into Thursday's face-off between Vice President Joe Biden and Wisconsin Rep. Paul Ryan.

They have become more popular among TV viewers.

The 1996 debate between Vice President Al Gore and former HUD Secretary Jack Kemp attracted 26.6 million viewers. The 2000 debate between former Defense Secretary Dick Cheney and Sen. Joe Lieberman drew around 29 million. But the debates have gotten more popular. The 2004 debate between Vice President Cheney and Sen. John Edwards brought in 43.5 million viewers, and the 2008 debate between Sen. Joe Biden and Alaska Gov. Sarah Palin had 69.9 million, according to Nielsen Media Research.

They are a major debut for vice presidential nominees.

After the announcement of the pick and a speech at the convention, the debates are the third and likely final opportunity for vice presidential picks to go before the public alone. For some, the results can be devastating. In 1992, Ross Perot's running mate, Adm. James Stockdale, stumbled badly when he began by asking "Who am I? What am I doing here?" Despite a sterling record as a military officer, his political reputation never recovered.

Poor showings can hurt a candidate for years.

In 1976, Sen. Bob Dole, the Republican nominee, argued during the debate about the number of Americans killed and wounded in "Democrat wars." His Democratic opponent, Sen. Walter Mondale, responded by saying Dole had "richly earned his reputation as a hatchet man." The line stuck to Dole for years afterward, causing many Republicans to doubt whether he could run for president effectively on his own, which he did unsuccessfully in 1996.

Some debates leave behind memorable quotes.

In 1988. Sen. Lloyd Bentsen squared off against Sen. Dan Quayle, the running mate for George H.W. Bush. Quayle, who had served for 12 years in Congress, argued that he had as much experience as John Kennedy had when he ran for president. Bentsen retorted: "Senator, I served with Jack Kennedy, I knew Jack Kennedy, Jack Kennedy was a friend of mine. Senator, you're no Jack Kennedy." -- a line that became so famous it has its own Wikipedia entry.

They can get very personal.

Vice presidential candidates often serve as attack dogs, so it's not surprising that when they get together things can get rough. Aside from Dole's cranky remark and Bentsen's takedown, one of the most personal attacks came in a roundabout way in 2004 when Edwards responded to a question about same-sex marriage by noting that Cheney's daughter is a lesbian. Cheney was gracious, but he later said he was furious that Edwards brought up his family in that way.

They usually don't matter much in the presidential race.

Like everything else in the presidential campaign, vice presidential debates get picked apart in the days afterward. But there's little evidence that they make much of a difference. Few people base their vote for president on the running mate and the debate plays a minor role in that. Despite its high ratings, the Palin-Biden debate wasn't seen as a major moment in the campaign. Most political observers expect this year won't be any different.

But this debate might matter more for the next election.

Biden is widely thought to be considering a run for the White House in 2016, but a poor showing at the vice presidential debate could hurt his chances in the Democratic primary. (If an Obama re-election loss doesn't first.) As early as 2010, many conservatives were pushing for Ryan to run for president, a move which he ruled out at the time saying he wanted to be "a normal person." If he becomes vice president, that excuse will no longer work. And even if Romney loses, a good debate showing would leave Ryan well positioned for his own run.